Q3.2 Buoyancy of Air

order of atmospheric layers

troposphere, stratosphere, mesosphere, thermosphere, exosphere

Atmosphere

A mixture of gases that surrounds a planet or moon.

Boyle's Law

A principle that describes the relationship between the pressure and volume of a gas at constant temperature

Why do scientists use kelvins?

Absolute zero. The Kelvin temperature scale is used by scientists because they wanted a temperature scale where zero reflects the complete absence of thermal energy.

Buoyancy of Air

One consequence of air pressure dependence on depth is the buoyancy of air. As with liquids, gases exert buoyant forces. An object surrounded by air is buoyed up by a force equal to the weight of the air displaced

Boyle's Law Equation

P1 V1 = P2 V2

Steel is almost eight times more dense than water. A steel ship can float in water instead of sink because of its

Shape. an object weighs less than the amount of water it displaces then it floats otherwise it sinks. A boat floats because it displaces water that weighs more than its own weight.

Does temperature measure kinetic energy?

Temperature is NOT a measure of total kinetic energy of a material. Temp measures the average movement or kinetic energy of the molecules. It does not measure how many molecules have this energy.

Say you have a balloon attached to the ground by a string. How many forces act on the balloon? Write an equation for the buoyant force, in terms of the vectors. Write an equation for the tension in the string.

The Buoyant force upwards, the weight (mg) downwards, and the tension (T) which keeps the system in equilibrium. BF = mg + T T = Bf - mg

The lowest temperature possible in nature is 0 degrees C. -273 degrees F -273 degrees C. 4 K

-273 degrees C.

A car driver measures a tire pressure of 220 kPa. What is the absolute pressure in the tire? Hint: The absolute pressure is the sum of the air pressure and the additional pressure measured inside the tire. Do you remember what the value of air pressure is so you can add it to the measured pressure of the tire?

321 kPa b/c 220kPa + 101kPa

Temperature

A measure of how hot or cold something is. All objects are warm in physics meaning it has kinetic energy/vibrates even if it solid. SCALAR QUANTITY. units: Kelvins, Fahrenheit, Centigrade

Density of helium

0.18kg/m^3

Density of air at normal temperatures

1.20 kg/m^3

at sea level, one cubic meter of air is the mass of about

1.25kg

At sea level, the atmosphere exerts a pressure of approximately

101,000 Pa, 101,000 N on every square meter, 10 N on every square centimeter

Atmospheric Pressure =

10^5 N/m^2 = 101.3 kPa (most used) = 1ATM = 14.7 lb/in^2

neon atom

10p+ 10n 10e-

Pressure exerted on a diver 10 m below the water's surface is twice the pressure at the surface. The pressure at this depth is

202 kPa

Ion

An atom or group of atoms that has a positive or negative charge by gaining or loosing one or more electrons. Ions have different number of electrons than protons, have a net charge that is not neutral or zero, may be attracted or repelled to other materials die to their electrical charge.

Buoyancy of Balloons

An object surrounded by air is buoyed up by a force equal to the weight of the air displaced. Ex. The atmospheric pressure at room temperature is 1m^3 and the object has a mass of 1.2kg. So, any cubic meter object is buoyed up w/a force about 12 Newtons. The object is buoyed up 12 Newtons. If the weight of the object is greater than the buoyant force, it will fall.

2b) How big would a helium-filled balloon have to be to lift Lillian? Neglect the buoyancy on Lilliam herself. (Density of helium is 0.18kgm^3)

BF = (mass of balloon + mass of Lillian)g BF = weight if displaced air density of air*g*volume of air = (mass of balloon + mass of Lillian)g Cancel out g's. density of air*volume of air = (mass of balloon + mass of Lillian) We don't know mass of helium. The volume of air and helium are the same so... density of air*volume = density of helium* volume + mass of Lillian Isolate volume on one side by reverse distribution. Volume = mass of Lillian / (density of air - density of helium). V = 48/(1.20-0.18)kg/m^3 = = 47m^3

A block of wood and a block of iron on weighing scales each weigh 1 ton. Strictly speaking, which has the greater mass? Block of wood, block of iron, or both

Block of wood. It has weight (mg or W) pushing down. It has a normal force (N) pushing up due to the weighing scale. The buoyant force (Fb) pushes up too. So, +N+Fb - W = 0 W = N + Fb Which ever object has the larger buoyant force, will have the larger weight. The buoyant force = weight of displaced fluid.

What will make the ball move upward? Blowing or inhaling through the funnel? Neither Inhaling Blowing

Blowing

Relationship between density, pressure, and temperature.

Density is directly proportional to pressure and indirectly proportional to temperature. As pressure increases, with temperature constant, density increases.

Surface Tension

The elastic tendency of a fluid surface which makes it acquire the least surface area possible. The water molecule surrounded by other H20 molecules experience cohesive forces from all directions. The surface molecules are pulled downwards into the body of water. When the water is sitting, there is gravity and surface tension cause it to move creating a flat surface.

Heat

The energy transferred between objects that are at different temperatures. Heat is not contained by an object. It is transferred energy or energy in transit. Objects contain INTERNAL ENERGY which may include both potential and kinetic energy.

Absolute Zero

The temperature at which no more energy can be removed from matter. Which all molecules have slowed down and come to rest. Corresponds to the molecules having no kinetic energy. Absolute Zeros of: F = -459 F C = -273.15 C K = 0 K

How are plasmas different from gases?

They contain both charged ions as well as free electrons. They readily conduct electricity. They absorb some forms of radiation that gases allow to pass through unhindered. They can be shaped and moved by electric and magnetic fields. ex. The sun - the hazy material around it is plasma. Neon signs - electric current runs through tubes where gases are electrified. Aurora Borealis and Aurora Australis - due to plasma in the sky.

Why is the top of an airplane's wing curved?

To create an area of low pressure above the wing. That shape makes air flow over the top faster than under the bottom. As a result, less air pressure is on top of the wing. This lower pressure makes the wing, and the airplane it's attached to, move up.

How are pressure and volume related?

Volume and pressure are inversely related

Centigrade

Water freezes at 0 C. Water boils at 100 C. 100 degrees between them. 1 C is larger than 1 F. The C scale is less sensitive to temperature changes.

Kelvin

Water freezes at 273.15 Kelvins. Water boils at 373.15 Kelvins. 100 Kelvins between them. 1K is larger than 1 F. 1 K is equal in size to 1 C. Kelvin is based on absolute scale.

Fahrenheit (US)

Water freezes at 32 F. Water boils at 212 F. 180 degrees between them.

Why don't we rise due to buoyant force?

We are heavier than the buoyant force.

1b) Lillian has a mass of 48kg. What approximate volume of air has the same mass as Lillian? (The density of air at normal temperatures is about 1.20 kg/m^3).

What is asked? Find the volume of air. From p=m/v. V = m/p, where p is density. 48kg /1.20 kg/m^3 = 40m^3. The approximate volume of air which is 40m^3 has the same mass as Lillian. It is a lot more then Lillian because air is much less dense then her.

How are pressure and volume of a gas related?

When the pressure of a gas at constant temperature is increased, the volume of the gas decreases. When the pressure is decreased, the volume increases.

Bernoulli Applications

Where the speed of a fluid increases, internal pressure in the fluid decreases.

Bernoulli's Principle

Where the speed of a fluid increases, internal pressure in the fluid decreases. Relates to air being blown above a piece of paper, airflow between vehicles, airflow between balloons, flight/lift forces (this principle may be disproved). Throwing a curve ball (low pressure on bottom of ball and high pressure on top of ball causing it to curve downwards). Roof during tornado. Ball and hair dryer

The atmospheric pressure at an altitude of 12,000 m is about one-fifth that at sea level. Airplanes that fly at this altitude pressurize the cabins for passenger safety. If these cabins were not pressurized, passengers would feel uncomfortable because the fluids inside their bodies would exert a pressure

approximately five times the pressure exerted on the outside of their bodies by the atmosphere.

An example of a fluid flowing during a change in pressure is

breathing., sipping a drink through a straw., opening a carbonated beverage.

Fluid pressure is exerted evenly in all directions, which explains why some objects float. birds and airplanes can fly. bubbles are round. objects seem to weigh less in water.

bubbles are round

Boyle's Law: PV =

constant. Decreasing volume increases collisions and increases pressure.

Plasma

electrified gas. The atoms and molecules that make up a plasma are ionized or stripped of one or more electrons which are then free to move independently.

Bernoulli's principle helps to explain

flight and flow. Lower pressure gives off bigger bubbles. Where the pressure is high, bubbles are smaller. Where the speed of a fluid increases, internal pressure in the fluid decreases.

Fluids flow from

from regions of high pressure to low pressure.

When you touch a cold piece of ice with your finger, energy flows

from your finger to the ice

A volume of water exerts greater pressure than the same volume of air because the water has more mass. is more dense. has more weight. all of these answers.

has more mass.

A helium-filled balloon will float in air because

helium is less dense than air.

low internal pressure of a fluid can cause

high pressure impact

Which of the following is NOT a fluid? Water Oxygen Oil Ice

ice

Bernoulli's Principle on a piece of a paper

if you hold two corners of the piece of paper, and blow air right above the piece of paper, it will rise up. Why is this? There is a higher velocity/lower pressure pushing down on the piece of paper and a lower velocity/higher pressure pushing up on the piece of paper. This results in a net force upwards

Fluid pressure is always directed

in all directions.

Upside-down wings, or spoilers, mounted on the rear end of race cars help to reduce the danger of accidents because they prevent the car from rolling. increase the air pressure below the car, decreasing lift. decrease the air pressure above the car, decreasing lift. increase the air pressure above the car, decreasing lift.

increase the air pressure above the car, decreasing lift.

An object displaces a volume of gas (or fluid) that

is equal to its own volume.

You may feel discomfort in your ears when you take off in an airplane because the pressure in your inner ear

is greater than the atmospheric pressure at a high altitude.

As you heat an object up,

its molecules start to move faster.

When you cool something down,

its molecules start to move slower

Sipping a drink through a straw that has been bent and cracked is difficult because air flowing through the crack

keeps the pressure high in the straw so there's not enough change in air pressure to allow the liquid to flow.

A bicycle tire feels harder as you pump more air into it because as you pump more air into the tire,

more air particles push against the walls of the tire, increasing the tire pressure.

If a fluid flows from area A to area B, then area A must be an area of greater

pressure

If you blow a steady stream of air between two sheets of paper, the papers will

the air between them is at a higher velocity and lower pressure than the air around them and they are pushed together. This is an application of the Bernoulli effect. move toward each other because the fast-moving air has a lower pressure than the air outside the pieces of paper.

Archimedes' Principle

the buoyant force on an object is equal to the weight of the fluid displaced by the object

Which of the following would NOT affect the level at which a cargo ship floats in a body of water? the shape of the ship the depth of the water the density of the ship's material the mass of the ship's cargo

the depth of the water

Astronauts wear pressurized suits in space because if they took their suits off,

the fluids in their bodies would overcome the pressure outside of their bodies, and they would explode.

atmospheric pressure

the pressure caused by the weight of the atmosphere 14.7 psi (atmospheric pressure at sea level). Atmospheric pressure decreases as you go up a mountain because there are fewer air molecules above you. The deeper down you go, the greater the pressure.